The proposed research outlines the use of quantitative approaches to studying dentine permeability. The ultimate goal is to develop methods and techniques of medicating pulpal tissues through intact dentin via topical application of appropriate substances. Permeability coefficients will be measured for a wide range of radioactive substances covering the molecular size range of 2-36 A in dentin that has been sanded, cut and acid-etched. This will include human adult coronal and root dentin as well as deciduous coronal dentin. Several techniques already shown to enhance dentin permeability in vitro will be evaluated in vivo in dogs. These include iontophoresis for ionized substances and bulk fluid movement (filtration). Both techniques will be used to increase dentin permeability in dogs in vivo. These same teeth will then be removed and the experiments repeated in vitro for comparative purposes. Scanning electron microscope studies will be done to correlate changes in dentin surface with functional changes in permeability. The SEM micrographs will provide direct measurements of dentin tubule dimensions. These will be compared to tubular dimensions calculated from filtration (hydraulic permeability) data which represent functional rather than anatomic dimensions. The permeability coefficients of adult human dentin to endodontic medicaments will be measured and compared to coronal dentin.